A device of this type is used, for example, in pressure filtration. In this method for the separation of solid/liquid mixtures the dried solid accumulates as bulk material in a pressure vessel, in which an overpressure several bar higher than the ambient pressure prevails. This bulk material generally accumulating continuously must then be discharged from the pressure vessel without an adverse effect on the actual filtration process. For this reason sluice systems with two sluice bins arranged one below the other are generally used, whereby the bins can each be closed in a gastight manner at their bottom ends by means of a sluice gate. Process pressure initially prevails in the two sluice bins, the top sluice gate being open, whereas the bottom one is closed in a gastight manner. The bulk material to be discharged is conveyed into the lower sluice bin until its maximum filling level is achieved. The top sluice gate is then closed in a gastight manner, so that pressure equalisation with the ambient pressure can be carried out in the lower sluice bin, whereas process pressure continues to prevail in the upper sluice bin. After emptying of the lower sluice bin by opening the bottom sluice gate, the latter is closed again and the sluice bin is again brought to process pressure. The top sluice gate is opened and a new sluicing cycle can start.
Rotary flaps, for example, are used as sluice gates. A rotary flap of this type comprises a sealing plate, which can be rotated about an axis, the latter running diametrically through the sealing plate and being arranged horizontally in the lower open end of the respective sluice bin. When the rotary flap is closed, the sealing plate assumes a horizontal position, whereby a seal running radially around the sealing plate rests on the inner wall of the sluice bin. To open the rotary flap the sealing plate is rotated about its axis of rotation into a vertical position, the first of the two halves of the sealing plate projecting upwards into the respective sluice bin, while the second half projects downwards from the sluice bin. Thereby the first half of the sealing plate must be moved against the bulk material lying on the sealing plate. On the one hand this requires quite a high drive power to open the sealing flap, while on the other it results in high wear on the seal in this area. Furthermore if the upper rotary flap is open, the second half of its sealing flap additionally projects downwards into the lower sluice bin. Consequently the maximum filling height of the lower sluice bin is reduced by the amount of the radius of the sealing plate. A dead volume, which must be ventilated or pressurised during each pressure equalisation, but is not available for the discharge of bulk material, thus results in the upper area of the sluice bin.
Flat slide valves can be used for the sluice gates as an alternative to the rotary flaps. These flat slide valves comprise a horizontal closing plate arranged in a casing, which can be moved horizontally in the casing between a first closed position, in which the closing plate closes a transfer duct for the bulk material arranged perpendicularly to the movement plane, and a second open position, in which the transfer duct is unblocked. To seal the transfer duct in the closed position, the closing plate interacts with a seal above it, which is fitted around the transfer duct in the casing. To allow absorption of the forces which the weight of the bulk material lying on the closing plate and the pressure prevailing above the closing plate exert downwards on the closing plate, the latter is generally mounted on supporting rolls, which are arranged around the transfer duct in the casing. As these forces added together produce a significant total force, the supporting rolls are exposed to an extremely high mechanical load. There is a risk that the total force will not be distributed uniformly to all supporting rolls and some of the latter will thus be loaded more heavily. This may lead to mechanical overstressing and fracture of their bearings. The sealing function fails, which in the event of fracture of several bearings leads to a sudden pressure drop in the pressure vessel and the associated reverse shock, which may lead to serious consequential damage to the entire system.